In the vicinity of transmitting antennae, particularly directional antennas, which are fed with frequencies ranging from 100 MHz to 100 GHz, high power densities of the electromagnetic field, may occur according to the transmitting power. These power densities may endanger the health of human beings on thermal grounds. In the Federal Republic of Germany, the permitted limits to the power density of distant field radiation so far as human beings are concerned are laid down by DIN 57 848 (VDE 0848, Part 2, August 1979) in accordance with similar specifications in other countries. A power density of 10 mW/cm.sup.2 for prolonged radiation is quoted in DIN 57 848 as the maximum value for the frequency range from 30 MHz to 30 GHz. A detailed substantiation of these anti-radiation provisions are presented by J. H. Bernhard in PTB-Mitt 90 (1980) 6, 416/433. In addition, in Paul Brodeur's book entitled "The Zapping of America", the risks to health of strong electromagnetic fields are discussed in detail. Protective suits are specified for people working in the vicinity of strong high-frequency electromagnetic fields having power densities above 10 mW/cm.sup.2. US Military Specification MIL-C-82296A is concerned with the quality of protective suits which allow people to remain in the power density range up to 200 mW/cm.sup.2 in the frequency range from 200 MHz to 10 GHz.
With such high power densities, particular problems are involved above all in the protection of low-circulation organs where overheating readily occurs. On page 62 of the above-mentioned book, it is stated, for example, that damage to the eyes has been caused by so-called cataract formation which may lead to blindness.
Protective suits complying with US Military Specification MIL-C-82296A consist of tightly woven, silver-coated textiles. Nothing is said about suitable eye protection which allows the passage of visible light. The protective goggles of narrow-mesh wire netting which are known from medical diathermy interfere with the sight and only afford adequate protection on account of the diffraction of the microwaves at the edges of the shield. Goggles in which electrically conductive glass is used as the shielding material are attended by similar disadvantages. For example, the permeability to light for a surface resistance of 10 ohms still amounts to 60%. For a surface resistance of 1 ohm, which would be necessary for screening 30 to 40 db, permeability to light falls to less than 40% (C. Rint, Handbuch fur Hochfrequenz- und Elektrotechniker, 1978, Vol 2, page 493).